package com.abner.design.patterns.interpreter;

import java.util.HashMap;
import java.util.Stack;

/**
 * 计算器
 * @author abner
 */
public class Calculator {

	/**
	 * 定义表达式
	 */
	private Expression expression;


	/**
	 * 构造函数传参，并解析
	 * @param expStr
	 */
	public Calculator(String expStr) {

		Stack<Expression> stack = new Stack<>();
		char[] charArray = expStr.toCharArray();

		Expression left = null;
		Expression right = null;

		for (int i = 0; i < charArray.length; i++) {
			switch (charArray[i]) {
			case '+':
				left = stack.pop();
				right = new VarExpression(String.valueOf(charArray[++i]));
				stack.push(new AddExpression(left, right));
				break;
			case '-':
				left = stack.pop();
				right = new VarExpression(String.valueOf(charArray[++i]));
				stack.push(new SubExpression(left, right));
				break;
			default: 
				stack.push(new VarExpression(String.valueOf(charArray[i])));
				break;
			}
		}
		this.expression = stack.pop();
	}

	public int run(HashMap<String, Integer> var) {
		return this.expression.interpreter(var);
	}
}